Introduction
Most desktop computers do or can run an X server. This is true
for X terminals, UNIX workstations and Windows PCs with an X
emulator such as Exceed.
When your desktop computer runs an X server you often need to
start remote X applications, i.e. applications not running on your
desktop but with the windows displayed on your screen. In some
cases this is transparent for you because XDM (the X Display
Manager) takes care of the details. In other cases some manual
intervention is needed.
This article explains how to start remote X applications (also
called X clients) easily and securely. This is the recommended way
to run remote X applications which need to be displayed at
CERN.
Note: the following recipes assume that your desktop is a
standard UNIX workstation (for instance, running CERN Red Hat
Linux). If you have a Windows PC or an X terminal you should first
login to a UNIX server (such as LXPLUS), using XDM, and then follow
the recipe.
Using ssh
The recommended way to start a remote X client is to use
ssh with its X11 forwarding feature enabled (this is
the default at CERN).
You can either start an interactive session with
ssh and start an X client (by simply typing the
command name) or directly start the remote command with:
ssh [-l <remote-user-name>] <remote-machine> <command> [<arguments>]
For instance:
ssh lxplus001 xload
ssh -l root myserver xterm -ls
See the ssh man page or http://cern.ch/security/ssh
for more information.
Using mxconns
If you can't use ssh, the other recommended way is
to use mxconns which is available on all standard UNIX
machines (through ASIS). Like ssh, it will relay the X
traffic to your X server.
The easiest solution is to start mxconns through
the HEPiX X11 scripts (by setting "HX_START_MXCONNS=yes" in your
~/.hepix/xprofile). This will take effect the next
time you login and will set the environment variable
XDISPLAY.
If you start it by hand, you should use:
setenv XDISPLAY `mxconns -fork -hunt -verbose`
Once connected to the remote machine (via ssh,
telnet, rlogin...), you should set the
DISPLAY variable on the remote machine to the value of
XDISPLAY on the machine where mxconns
runs. For instance:
setenv DISPLAY lxplus002.cern.ch:9
You can then start your remote X client.
Note: the preceding commands assume that you are using
tcsh. If you are using the Bourne shell then the
command is:
DISPLAY=<whatever>; export DISPLAY
See the mxconns man page or http://cern.ch/mxconns
for more information.
About the author(s):
Lionel Cons is a member of the CERN security team (Computer.Security@cern.ch).
